1. Field of the Invention
The present invention relates to an injection mold design system and an injection mold design method and, more particularly, a design support system for a mold used for fabricating resin (plastics) injecting moldings and a design method for designing the mold.
2. Description of the Related Art
In recent years, according to demands for more variety of product design, users' various usages etc., plastics have been widely used as material of enclosures for electrical products since they may present an attractive appearance and may be molded arbitrarily. In addition, it entails such advantages that reduction in the number of parts and simplification of assembly may be attained. This is because seats, bosses (projections), etc., these being used for mounting printed circuit boards and other parts, and reinforcing members such as ribs may be formed integrally with the enclosures if the enclosures are fabricated by resin injection molding.
FIG. 1A shows an example of moldings (molded products) formed by resin injection molding. In FIG. 1A, a reference 1 denotes a molding used as an enclosure of a portable electronic device, and a reference 2 denotes a bore portion provided in the molding 1. After preparing the mold in which a cavity having the same profile as that of the product is in advance formed, melted resin is filled into the cavity and then cured, so that the molding 1 with a shape shown in FIG. 1A may be formed. At this time, the bore portion 2 may be formed by nests arranged in the mold.
FIG. 1B shows a configuration of the mold. In FIG. 1B, a reference 3 denotes a cavity (female mold) for defining an outer shape of the molding 1, and a reference 4 denotes a core (male mold) for defining an inner shape of the molding 1. When the cavity 3 is put on the core 4, the cavity corresponding to the products profile to be formed may be formed between them.
FIG. 1C shows a configuration of an injection molding machine on which the mold is mounted. With being arranged so as to oppose to each other in the vertical direction, the cavity 3 and the core 4 are clamped on a cavity plate 3A and a core plate 4A respectively. The cavity plate 3A may be driven by a driving apparatus (not shown) to move in the vertical direction. A reference 5 denotes a runner stripper plate in which a runner (not shown) is formed to introduce the resin 7 into the space in the mold. The runner stripper plate 5 may be placed on the cavity plate 3A. When the molds are opened, the runner stripper plate 5 may then be separated from the cavity plate 3A to enable the resin cured in the runner to be removed from the runner. A reference 6 denotes a gate (pouring gate) formed in the mold. Resin 7 is filled into the cavity in the mold via the gate 6.
A reference 8 denotes a gas vent (breathing hole) which is provided in the mold to exhaust the air from the space in the mold to the exterior when the resin is poured into the space in the mold. A reference 9 denotes a cooling water path provided in the mold. Since the resin to be filled into the mold is heated at a temperature of a few hundreds .degree. C., a temperature of the mold is raised when the resin is filled into the mold. As a result, drawbacks such as not only reduction in molding efficiency but also warpage, twist, etc. of the product are caused. In order to prevent the drawbacks, the mold is cooled by flowing water through the cooling water path 9. Usually, the cooling water path 9 is provided on the core 4 side.
A reference 10 denotes an extruder portion for extruding the moldings 1 from the core 4. The extruder portion 10 has a rod-like member referred to as an ejector pin. The moldings 1 can be extruded from the core 4 by inserting the ejector pin into a through hole provided in the core 4.
In any event, since the injection mold is composed of the cavity 3 and the core 4, as mentioned above, the mold must be split into the cavity 3 side and the core 4 side when designing the mold. The split plane is called a parting plane. In case there is caused an undercut portion in the products to be fabricated, the moldings cannot be stripped off from the mold if the parting plane is set incorrectly. Here the undercut portion may be defined as a portion serving as an engagement formed in the mold opening direction when the product is taken out from the molds. If the undercut portion exists, consideration for providing a slide structure to the mold or the like should be taken inevitably.
In order to strip the product off from the mold readily, slight slopes (draft slopes) are provided on the surface of the mold so as to prevent inner surfaces of the mold from being formed perpendicularly to the parting plane. In the prior art, in the case of the mold having a relatively simple profile, mold designers be able to design the mold according to drawings prepared for the product while considering parting plane, draft slope, etc. Conversely, as for the product which must be designed by use of a plenty of free-form surfaces to achieve the high design property, it would become difficult to illustrate the profile of the product in the drawings. As a countermeasure to this drawback, first the product model (model) is formed, then profile lines of the product model are illustrated with many dots, and then the profile of the product is converted into numeric data by correlating these dots with each other in terms of digitizing process. Then NC (Numeric Control) data used for cutting process and electric discharge machining electrodes are then prepared for based on the numeric data. According to these data, the mold may be then fabricated by the electric discharge machining electrodes.
In the meanwhile, there are some cases where the mold may be designed by means of the three dimensional CAD (Computer-Aided Design) system. In such cases, data of the product shape are first input into the CAD system, then the product shape or the mold block (i.e., virtual block displayed on the screen for illustrating an outer shape of the mold) in which a cavity corresponding to the product shape is formed is depicted on the display. While monitoring the screen of the display, the designer may draw the parting line on the screen to form the parting plane or select the planes to which a draft slope is provided. The CAD system may thus output numeric data to form the mold in compliance with these setting conditions.
However, in the method where the designer has to design the mold on the basis of the design drawings, the designer must design the mold while considering undercut, draft slope, etc. as mentioned above. Therefore, it can be seen that, in the case of the product with complicate profile, it would become difficult for the designer to determine a solid product shape from the drawings. For this reason, according to this method, problems have been arisen that man-hour in design is increased and design error is prone to generate. Alternatively, in the method where data used for fabricating the mold are generated from the product model, there are some problems that, since the product model must be formed to have a precise profile, the designer must be well practiced in forming the product model and much time must also be consumed to form the product model.
Moreover, in the method where the three dimensional CAD system is used, the troublesome procedures would be required and further a great deal of skill would be required for the designer since the mold designer must design parting plane, draft slopes, etc. on the basis of image displayed on the screen of the display. Because of the causes such as missing of the undercut portion, the mold designer is apt to generate errors in design.